The present invention generally relates to a tube joint for fuel tanks made of resin materials.
In recent years, plastic containers produced by blow molding have been used as a fuel tank of vehicles as they excel in rust preventative characteristics and weight reduction as well as their high productivity.
Various parts are attached to the tank body of the fuel tank through a tube joint. These parts include, for example, a vent valve, a check valve, and a fuel pump. The vent valve retains the internal pressure of the tank body at a certain level by discharging fuel evaporation gas that is held in a space above the oil level from the tank.
In the case where the tank body and the tube joint are both produced by the same kind of synthetic resin, such as high density polyethylene (hereinafter referred to as “HDPE”), they can be jointed by heat welding. This can simplify the manufacturing process of the fuel tank.
Since effusion of the fuel evaporation gas from the fuel tank causes air pollution, the tank body and its joint portion require low hydrocarbon permeability (hereinafter referred to as “fuel impermeability”). However, synthetic resin such as HDPE is relatively poor in fuel impermeability. For this reason, to restrict the permeation of hydrocarbon, it is considered to use so-called gasoline barrier materials having excellent fuel impermeability, such as ethylene-vinylalcohol copolymer (hereinafter referred to as “EVOH”). However, these gasoline barrier materials are poor in adhesion properties upon heat welding and difficult to satisfy the joint strength between the tank body and the tube joint.
To be more specific, the tube joint fixed to the tank body of the plastic fuel tank is preferably made of a material which has sufficient strength and rigidity, excellent gasoline swelling resistance and high fuel impermeability, and further which can be heat welded to the tank body. However, it is very difficult to produce this tube joint by a single material. Therefore, as disclosed in Japanese Laid-open Patent Application No. 2002-254938 (claim 1, paragraphs [0006] to [0010], and FIG. 1), the tube joint (weld joint for the fuel tank) is integrally formed by coinjection molding two kinds of resins.
FIG. 3 shows a sectional view partly and schematically showing a conventional tube joint of a fuel tank. As shown in FIG. 3, the tube joint 110 fixed to the tank body 100 of the fuel tank consists of a tubular joint body 120 and a barrier layer 130 for covering the inner surface of the joint body 120. The joint body 120 is made of a first resin material weldable to the tank body 100, and the barrier layer 130 is made of a second resin material that is adhesively and chemically reactive with the first resin material and that has better fuel impermeability than the first resin material. The barrier layer 130 is provided with an end portion 131 that protrudes from the distal portion 121 of the joint body 120. Upon injection molding the barrier layer 130 on the inner surface of the joint body 120, the end portion 131 is formed by the flow of the second resin material flowing from the proximal portion 122 of the joint body 120 that is fixed to the tank body 100 and through the distal portion 121. The end face 140 where the end portion 131 and the distal portion 121 are joined together does not dispose in the end for the flow of the second resin material, and the second resin material is welded at a high temperature to the joint body 120. This can provide a high degree of adhesive strength between the end portion 131 and the distal portion 121. The tube joint 110 formed as above allows the joint body 120 to be heat welded to the tank body 100 as well as decreases the fuel permeability of the barrier layer 130 that covers the inner surface of the joint body 120.
However, the above tube joint 110 has a drawback such that when a tube 150 is connected to the tube joint 110, the fuel within the tank body 100 permeates outside from a gap between the tube joint 110 and the tube 150 or water droplets enter into the tank body 100 from the gap. Further, if a sufficient adhesion is not obtained between the different kinds of resin materials, the adhered surfaces may be peeled, leading to the entry of water droplets into the tank body 100.
The tube 150 is inserted onto the end portion 131 of the tube joint 110 and thereafter engaged by a clamp by firmly clamping the outer periphery of the tube 150, so that the tube 150 is not pulled out from the tube joint 110. However, since the tube 150 is only supported between the two tubular surfaces, the tube 150 is pulled out relatively easily when it is pulled hard.
In view of the above, the present invention seeks to provide a tube joint of a fuel tank, which can firmly clamp the tube and which can provide a sufficient seal.